Abstract
The rice lamina joint inclination assay is well known as an extremely sensitive system for brassinosteroid (BR) bioassay, although it was originally developed as an assay for auxin. The synergy between BR and auxin in the rice lamina joint inclination assay has also been reported, however, the molecular mechanism of this synergism has remained elusive. Here we demonstrate that auxin treatment transiently increases the expression of the rice BR receptor gene, OsBRI1, and its translational product, OsBRI1. The other phytohormones, such as gibberellin, cytokinin, and jasmonic acid did not affect the expression of OsBRI1, although the BR treatment decreases the expression of OsBRI1. On the other hand, auxin treatment did not affect the expression of BR biosynthetic and catabolic enzyme genes. These results suggest that auxin stimulates the BR sensitivity by increasing the expression of BR receptor, OsBRI1.
